Terrifying Teammate

I don’t know what effect they have on the enemy, but by the Emperor, they frighten me.

—Sandy Mitchell, Ciaphas Cain

Maybe he is a Team Killer. Perhaps his ruthlessness is horrifying no matter what side you're on. Or maybe his teammates suspect he takes enjoys combat a little too much or in the wrong way. Maybe he just seems creepy. Regardless of the reason, this is a character that is feared, and sometimes reviled, by his own side. Is the enemy of his side scared of him? Not always. Perhaps the enemy has simply never seen this monster in action yet, or at least those that have haven't lived to talk about it, including those that surrendered.

In some cases there can be several of these in the same unit (perhaps the entire unit) who might not scare those not in the unit, but scare other members of the same side. (In this case the members can be similar enough that they probably aren't really considered individuals.) Simply scaring one person on the same side is not sufficient (unless that faction is really small), this character must at least instill a respectable amount of fear in a sizable part of his own faction. In some cases this trope might be exploited by one of the sides, for example Outscare the Enemy.

May be a result of Even Evil Has Standards. Likely to overlap with The Dreaded.

Examples of Terrifying Teammate include:

Anime and Manga

Gaara in Naruto, he softens up though. To make things worse, his teammates are his actual siblings. It's probably safe to assume he scares other sand ninja as well. Also Kimimaro’s clan feared him, so they locked him up when they weren’t in battle.

Comic Books

Subverted by Wolverine in the Marvel Universe, at least since the 1980s or so -- he's just this big rough-edged teddy bear who's loved by everyone who, well, occasionally goes berserk and kills people. Lots of people.

Tabletop Games

Sanctioned Psykers in Warhammer 40,000 have a tendency to be hated and feared by there own side. The Imperium also sometimes makes use of Outscare the Enemy (often done by commisars). Also the Inquistion generally receives a great amount of both admiration and fear.

Video Games

Team Fortress 2: The Pyro in the Meet the Pyro video. The video opens up with its teammates talking about what a terrifying inhuman freak it is.